Groups from the Solid State Physics Laboratory (LPS) and INSERM group 606 used the DIFFABS beamline at SOLEIL to analyze a series of cartilage samples taken from 6 patients who underwent total knee joint replacements for OA.
Figure 1 : Knee joint specimen obtained during arthroplasty and schematic representation of the sample collection protocol. The specimen included femoral condyle and tibial plateau cartilage
from both the medial and the lateral compartments.
Cartilage areas were labelled as follows: 1, medial condyle; 2, lateral condyle;
3, medial tibial plateau; 4, lateral tibial plateau; S, superficial layer; D, deep layer.
The implication of abnormal mineralization of the cartilage is more and more frequently mentioned in osteoarthritis pathogeny. However, little is known about how these calcium compounds are involved in the mineralization process. To improve our understanding, first, infrared spectroscopy measurements were taken at the Necker Hospital (AP-HP) in order to look for possible crystals in the cartilage samples containing calcium ions (Ca2+) and to study their biochemical composition. During a second stage, the samples were analyzed on the DIFFABS beamline, using X-ray absorption spectroscopy (XAS) at the Ca2+ K-absorption edge in order to determine under which biochemical form the calcium compounds identified are found. This XANES technique proved to be perfectly adapted to the characterization, in human cartilage samples, of isolated calcium compounds.
The data obtained showed that the calcium compounds differed depending on the area of analyzed cartilage. In the calcified areas, they were Ca2+ crystals (calcium phosphate or pyrophosphate dihydrate crystal deposits or CPPD).
It appears that in what form the calcium was found was an integral part of the calcification, thus modifying the biochemical equilibrium within the joint. It should be noted that calcification is equally present within the cartilage and in this case it cannot come from a simple precipitation of joint fluid, but probably as a result of the malfunction of chondrocyte cells present in the cartilage.
Results published in: “Calcifications in human osteoarthritic articular cartilage: ex vivo assessment of calcium compounds using XANES spectroscopy”. Nguyen, C., Ea, H.K., Thiaudiere, D., Reguer, S., Hannouche, D., Daudon, M., lioté, F. & Bazin, D., J. Synchrotron Rad. (2011) 18. DOI:10.1107/S0909049511006984
